Can't write/read 16 bit register addresses on npm1300 through i2c

Question

I'm trying to demonstrate that I can write a value to a Nordic npm1300 register and read the same value back. Using the code below, I write 0x5a but read 0x0a, so the msb 5 is getting lost: 
 
 uint8_t pmic_config [] = { 0x06 , 0x01 , 0x5a }; //register followed by value 
 ret = i2c_write_dt ( & dev_i2c_pmic , pmic_config , 2 ) ; 
 if ( ret != 0 ) 
 { 
 printk ( "Failed to write pmic register %x 
 " , pmic_config [ 0 ]) ; 
 return - 1 ; 
 } 
 
 //read something from the pmic 
 int myVal = 0 ; //this will be returned 
 uint8_t regsy [] = { 0x06 , 0x01 }; 
 
 ret = i2c_write_read_dt ( & dev_i2c_pmic , regsy , 2 , & myVal , 1 ) ; 
 if ( ret != 0 ) 
 { 
 printk ( "Failed to read pmic register %x%x 
 " , regsy [ 0 ], regsy [ 1 ]) ; 
 return - 1 ; 
 } 
 else 
 { 
 printk ( "pmic Register 0x %x%x is 0x %x 
 " , regsy [ 0 ], regsy [ 1 ], myVal ) ; 
 } 
 
 Result: 
 pmic Register 0x61 is 0xa 
 
 All the solutions I saw posted here used nrf_drv_twi_tx and nrf_drv_twi_rx which seem more complex than i2c_write_read_dt(), so it would be nice if there's a simple solution involving the code I shared above.

SergeiOv · Accepted Answer

If you look at the description of the register you are attempting to write (address 0x0601 corresponds to https://docs.nordicsemi.com/bundle/ps_npm1300/page/chapters/core_components/gpio/doc/frontpage.html#ariaid-title6 ), you can see that it uses only the lower 4 bits, so the msb 5 in your case is simply ignored. And yes, the number of bytes to write in the ` i2c_write_dt ` should be equal to the array size. 
 To get an idea of how to communicate with the PMIC through I2C it is worth taking a look at how the mfd_npm13xx driver implements this: github.com/.../mfd_npm13xx.c

kruenheck · Answer

Thank you, the problem was that I was writing/reading a four bit register.

Can't write/read 16 bit register addresses on npm1300 through i2c

Top Replies